Synthesis, Characterization And Hydroprocessing Performance Of A Novel Catalytic Material-Tungsten Phosphide

In view of more stringent environmental legislation and the growing increase content of heteroatoms in fuel, it is more important for optimization and clean utilization of oil to keep the sustainable development of economy and sociality. The traditional transition-metal sulfide catalysts could not meet needs of the people for lower content of sulfur and nitrogen in fuel. To meet these demands, either existing catalysts have to be improved, or alternative catalysts and technology have to be found, which is an effective way to produce the clean fuels and solve the pollution problems from the automobiles. It has important theoretical and practical meaning to study synthesis, characterization and hydroprocessing performance of a novel catalytic material-tungsten phosphide.Unsupported and supported WP catalysts were prepared by the method of temperature-programmed reduction of phospho-tungstate in H₂ and characterized by XRD, BET, NH₃-TPD, TG/DTA, SEM, ³¹P MAS-NMR. The synthetic mechanism of the catalysts was studied. The hydrodesulfurization(HDS) and hydrodenitrogenation(HDN) activities of the catalysts were tested by thiophene, pyridine, dibenzothiophene, quinolin and carbazole as the model compounds. The effect of promoter and support on thestructure and catalytic activities was investigated. The path ways of dibenzothiophene HDS and carbazole HDN on WP/y-A12O3 catalyst were studied and the sulphur-resistant ability of the catalyst was also discussed 0 The main work is as follows:1 . Unsupported and supported WP catalysts were prepared by temperature-programmed reduction of phospho-tungstate in H2. The effects of promoter, preparation method and support on structure and catalytic activities of the catalysts were investigated. The industrial catalyst was phosphided successfully by the same method.2. Bulk phase and surface species of WP were characterized by various methods. XRD and 31P MAS-NMR results indicated that crystal structure of WP could not be changed by passivation. WP was a pore material and had weak acidity on the surface. W species existed in W8+ and W6+ state and P species existed in of P° and P5+ state, in the meantime a little P existed in the P8" state on the passivated WP surface. Adding of promoter Co and Ni caused the surface area of WP to decrease to some extent and P8" on the WP surface to disappear. P/W atomic ratio on the Ni-WP catalyst surface was higher than that on WP surface, while P/W atomic ratio on the Co-WP catalyst surface was lower than that on WP surface.3. WP/y-Al2O3 catalysts prepared by different method were characterized. The dispersion of the active species on the surface of catalyst prepared by impregnation method was higher than that by mixing method. The surface area of the WP/y-A12O3 catalyst prepared by mixing method was larger thanthat by impregnation method. Co-WP/y-Al2O3 catalyst prepared by impregnation method showed higher surface area than Ni-WP/y-Al2O3 catalyst when the content of promoter cobalt and nickel was the same. XPS results showed that P° disappeared on the passivated WP/y-Al2O3 catalyst surface. The amount of W6+species on the surface of the WP/y-Al2O3 catalyst prepared by impregnation method was over two times high as catalyst prepared by mixing method. The promoter cobalt and nickel were favourable to increasing the amount of W species existing in lower valence state on the surface of the WP/y-Al2O3 catalyst prepared by impregnation method.4. The synthetic mechanisms of WP and WP/y-Al2O3 catalysts were investigated by TG/DTA method. It was found that the reduction-phosphiding process of tungsten phosphide catalyst precursors was one step reaction. The WP precursor could be completely reduced to WP at temperature range of 650—700°C and WP was stable until 900°C in H2. The oxygen on the WP surface induced during the passivation process could be removed in H2 at temperature range of 528°C-613°C. The starting reduction-phosphiding temperature of WP/y-Al2O3 catalysts was lower than that of WP catalyst. Due to the stronger interaction of support with active species, the WP/y-Al2O3 catalyst precursor prepared by impregnation method was more difficultly to be deeply reduced and phosphided than that prepared by mixing method and the species with structure similar to -Al-O-W-P may be formed. A certain content of promoter cobalt caused the WP/y-Al2O3 catalyst precursor to be easily reduced and phosphided to some extent and the startingreduction-phosphiding temperature decreased by adding a certain content of promoter nickel. Promoter may had an effect on the interaction of support with active species for the WP/y-Al2O3 catalyst.5. The experiment results of thiophene HDS and pyridine HDN of the WP/y-Al2O3 catalyst showed that higher reaction temperature was favourable to thiophene HDS reaction and lower reaction temperature was favourable to pyridine HDN reaction. The WP/y-Al2O3 catalysts prepared by impregnation method possessed higher thiophene HDS activities and lower pyridine HDN activities than those of the WP/y-A12O3 catalysts prepared by mixing method. The WP/y-Al2O3 catalyst with species of -Al-O-W-P structure due to stronger interaction of support with active species had a higher HDS activity, while the WP/y-Al2O3 catalyst with some WP species due to weaker interaction of support with active species had a higher HDN activity. A certain amount of promoter nickel and cobalt could improve the thiophene HDS activity of WP/y-Al2O3 catalyst. A certain content of promoter cobalt had a positive effect on the pyridine HDN of WP/y-Al2O3 catalyst, while promoter nickel showed a negative influence on the pyridine HDN of WP/y-Al2O3 catalyst. The effect of support on thiophene HDS activity of supported WP catalyst was investigated, which showed that the activity order was WP/y-Al2O3> WP/SiBAPO-5> WP/SiO2. The supported WP catalyst prepared using a support that had a certain surface acid amount and a higher interaction with active species had a better thiophene HDS activity.6. WP/y-Al2O3 catalyst prepared by impregnation method had a highdibenzothiophene(DBT) HDS and quinolin HDN activity, also had a high carbazole HDN activity at high reaction temperature. A certain amount of nickel or cobalt in the WP/y-Al2O3 catalysts had positive effect on DBT HDS at suitable reaction temperature, especially on carbazole HDN activity at lower reaction temperature. The CO-WP/Y-AI2O3 catalyst with 5% cobalt showed higher diesel HDS activity than sulphided industrial NiW/y-Al2O3 catalyst, which indicated that this catalyst had better deep HDS potential.7. DBT HDS reaction on WP/y-Al2O3 catalyst prepared by impregnation method had two path ways: direct desulfurization and hydrodesulfurization. The direct desulfurization was the main path way. The selectivity of direct desulfurization were improved by adding 3% promoter nickel or cobalt to the WP/y-Al2O3 catalyst and reached a level of 64.5% and 61.7% at high reaction temperature, respectively. The high reaction temperature was favourable to direct desulfurization. Carbazole HDN reaction on WP/y-Al2O3 catalyst prepared by impregnation method had three path ways: direct denitrogenation, denitrogenation after hydrogenation of one benzene ring and denitrogenation after hydrogenation of two benzene rings. The third was the main path way, which selectivity achieved over 91.0%. The selectivity at high reaction temperature of the third path way was 61.6% and 77.8% by adding 5% of nickel and cobalt to the WP/y-Al2O3 catalyst, respectively.8. Resistance to sulfidation for WP in thiophene HDS reaction and for WP/y-Al2O3 catalyst prepared by impregnation method in sulfiding treatment and long time (200h) thiophene HDS reaction were investigated by XPS and...